refactor: hashing service (#21997)

* download only backup selected assets

* android impl

* fix tests

* limit concurrent hashing to 16

* extension cleanup

* optimized hashing

* hash only selected albums

* remove concurrency limit

* address review comments

* log more info on failure

* add native cancellation

* small batch size on ios, large on android

* fix: get correct resources

* cleanup getResource

* ios better hash cancellation

* handle graceful cancellation android

* do not trigger multiple hashing ops

* ios: fix circular reference, improve cancellation

* kotlin: more cancellation checks

* no need to create result

* cancel previous task

* avoid race condition

* ensure cancellation gets called

* fix cancellation not happening

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: mertalev <101130780+mertalev@users.noreply.github.com>
Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/ios/Runner/Sync/PHAssetExtensions.swift

@@ -0,0 +1,77 @@
+import Photos
+
+extension PHAsset {
+  func toPlatformAsset() -> PlatformAsset {
+    return PlatformAsset(
+      id: localIdentifier,
+      name: title,
+      type: Int64(mediaType.rawValue),
+      createdAt: creationDate.map { Int64($0.timeIntervalSince1970) },
+      updatedAt: modificationDate.map { Int64($0.timeIntervalSince1970) },
+      width: Int64(pixelWidth),
+      height: Int64(pixelHeight),
+      durationInSeconds: Int64(duration),
+      orientation: 0,
+      isFavorite: isFavorite
+    )
+  }
+
+  var title: String {
+    return filename ?? originalFilename ?? "<unknown>"
+  }
+
+  var filename: String? {
+    return value(forKey: "filename") as? String
+  }
+
+  // This method is expected to be slow as it goes through the asset resources to fetch the originalFilename
+  var originalFilename: String? {
+    return getResource()?.originalFilename
+  }
+
+  func getResource() -> PHAssetResource? {
+    let resources = PHAssetResource.assetResources(for: self)
+
+    let filteredResources = resources.filter { $0.isMediaResource && isValidResourceType($0.type) }
+
+    guard !filteredResources.isEmpty else {
+      return nil
+    }
+
+    if filteredResources.count == 1 {
+      return filteredResources.first
+    }
+
+    if let currentResource = filteredResources.first(where: { $0.isCurrent }) {
+      return currentResource
+    }
+
+    if let fullSizeResource = filteredResources.first(where: { isFullSizeResourceType($0.type) }) {
+      return fullSizeResource
+    }
+
+    return nil
+  }
+
+  private func isValidResourceType(_ type: PHAssetResourceType) -> Bool {
+    switch mediaType {
+    case .image:
+      return [.photo, .alternatePhoto, .fullSizePhoto].contains(type)
+    case .video:
+      return [.video, .fullSizeVideo, .fullSizePairedVideo].contains(type)
+    default:
+      return false
+    }
+  }
+
+  private func isFullSizeResourceType(_ type: PHAssetResourceType) -> Bool {
+    switch mediaType {
+    case .image:
+      return type == .fullSizePhoto
+    case .video:
+      return type == .fullSizeVideo
+    default:
+      return false
+    }
+  }
+}